1. Technical Field
The invention relates to pneumatic tires and particularly to a bead construction molded into the pneumatic tire sidewalls for mounting the tire on a rim. More particularly, the invention relates to a helically wound bead having an offset bending so that the bead sidewalls when in wound position, will remain in a pair of substantially flat parallel planes, thereby improving tire uniformity.
2. Background Information
Pneumatic tires for automobiles generally consist of a crown or tread area which comes into contact with the road surface, and a sidewall on either side of the crown, which terminates at an inner edge which is supported by the rim of a wheel. An annular bead is molded within the terminal edges of the sidewalls to function as an anchorage for the plies forming the carcass of the tire and to ensure a seal between the tire and wheel rim. Various types of bead constructions have been used in the manufacture of pneumatic tires, such as cable rings formed of wire of substantially circular cross-section, and beads in which the strand is wound helically around a core until the desired cross-sectional thickness is achieved. In the formation of the tire beads, splices are produced which can result in non-uniformity in the tire which effects the ride characteristics of the tire. Helical wound beads reduce this non-uniformity produced by heretofore spiral wound bead wires, but still produce some non-uniformity due to the ends of the spiral producing a pair of side laps. Although these helical wound beads increase tire uniformity, it is still desirable to achieve greater uniformity by eliminating the non-uniformity caused by the terminal lapped ends of the helical wound bead wire.
The use of a helical wound bead wire to increase tire uniformity has been recognized in the prior art.
For example, Australian Patent No. 518053 discloses a bead component for a pneumatic tire in which a conventional flat steel wire is wound into a plurality of layers in their direction of thickness, wherein the generally rectangular longer portions of the wire are in abutment with each other.
French Patent No. 1,418,887 discloses a bead area for a tire which is reinforced by a plurality of beads arranged in a circular configuration as opposed to a helical wound bead.
U.S. Pat. No. 3,949,800 discloses a tire bead having a generally rectangular cross-sectional wire, in which each bead ring is comprised of a plurality of these wires which are wrapped adjacent to one another in multiple turns about the tire, in order to form a generally parallelogram type cross-section.
U.S. Pat. No. 4,290,471 discloses another pneumatic tire having a built-up core formed by a plurality of wires wound about one another. The individual wires have a trapezoidal shape to provide clearance spaces between adjacent wires.
U.S. Pat. No. 1,231,446 discloses a tire bead formed from a continuous strip of wire in which the ends of the material have two oblique cuts which are adapted to abut similar cuts on adjacent strips.
Other prior art bead construction which attempt to reduce this non-uniformity caused by splices and side-lap ends are also shown in the following patents.
U.S. Pat. No. 1,512,795 discloses a tire bead comprising a ribbon or hoop formed from a single flexible wire which is bent into a plurality of convolutions and which has a flat or ribbon-like cross-section. The cord is wrapped around itself to unitize the bead. The ends of the wire then are brazed, welded or soldered, or a sleeve is positioned over the wire.
U.S. Pat. No. 1,713,871 discloses a reinforcing tire bead in the form of a steel tape having rounded edges. The strip is formed from metal and is wound in a rather long spiral with one winding or convolution over a predetermined distance.
U.S. Pat. No. 3,170,662 discloses a pneumatic tire having a bead in which the bead core comprises a plurality of convolutions with the leading end being formed as a radially inner end of the bead grommet. The wire is cut at a plurality of longitudinally spaced locations so that the distance between adjacent endings is preferably equal to or greater than the width of the wire. The trailing ends of the wire are cut in a complementary fashion with respect to the leading ends of the wire, so as to form a plurality of wire endings which are spaced apart by a distance which is at least equal to and preferably greater than the width of the wire. The forming of these complementary-shaped ends is to form a bead with substantially parallel inner and outer surfaces to avoid end lap.
Japanese Patent No. 58-128906 discloses a bead ring having a stabilized shape of a plurality of flat wires, having vertically opposed parallel sides. Round wires are positioned between the flat wires so that they will contact the vertical surfaces of the flat wires. In this manner, the wires are wound in a plurality of layers, so that the bead ring is formed as having rounded corner sections.
German Patent No. 3,247,441 discloses a plurality of beads produced by winding a plurality of high tensile-strength wires on a winding drum. The outside of each of the cords is aligned with a profiled strip of unvulcanized rubber, which is adapted to fit into a corresponding strip on an adjacent bead.
Thus, although the prior art recognizes that a helical wound pneumatic tire bead is preferable in many applications to reduce tire non-uniformity, the problem still exists in producing such a bead in a satisfactory and economical manner, without the still inherent overlap caused by the terminal ends of the helical wound wire.
This end overlap has been eliminated in other non-analogous art, such as shown in Japanese Utility Application No. 15438/85, wherein a spring roller for use as a bushing in a drive-chain of a bicycle or motorcycle, is initially wound into a coil shape. The ends then are pressed so that the opposite end faces become planar. These bushings are then placed between the individual links of the drive chain.
However, there is no known prior art of which I am aware which discloses or suggests the formation of a helical wound bead wire for use in pneumatic tires which reduces or eliminates non-uniformity heretofore resulting from a side lap, by crimping or offset bending the helical wound wire over a distance such that the bead sidewall when wound will remain in a substantially flat plane, rather than being angled or inclined along the opposite sides thereof.